This invention relates to a means for measuring mass flow of fluid materials such as liquids, gas and fluid solid material wherein coriolis force is utilized as an indication of the mass flow. The flowmeter includes U-shaped tubes which are vibrated while a fluent material to be measured flows through the tubes. Means are included to measure the mass flow of the material flowing through the tubes responsive to the vibrating characteristic of the tubes as altered by coriolis forces acting on the tubes.
U.S. Pat. No. 2,865,201 to Roth discloses a mass flowmeter of the giroscopic type which includes an embodiment illustrated in FIG. 6 of that patent wherein the amplitude of the precession of the giroscopic flowmeter is measured to give an indication of the mass flow through the meter. It is generally recognized that precession in a giroscope is caused by coriolis force.
A patent to Sipin, U.S. Pat. No. 3,355,944, discloses measuring the amplitude of twist in a curved flow tube induced by coriolis force to determine the mass of material flowing through the meter.
A giroscopic/coriolis flowmeter developed by Micro Motion, Inc. of Boulder, Colo. is described at page 21 of the Dec. 19, 1977 volume of Chemical and Engineering News. The flowmeter includes a U-shaped pipe with a T-shaped leaf spring to form the legs of a tuning fork. The pipe is vibrated at its natural frequency and the angular deflection is measured with optical detectors.
The optical detectors are placed on the sides of the U-shaped pipe and are connected to an up-down counter such that when one side of the U-shaped pipe crosses the static plane, the counter counts down until the second side of the pipe crosses the static plane. In the following half cycle of the vibration of the U-shaped pipe, the up-down counter counts up during the interval between the passing of the first side and the second side of the U-shaped pipe crossing the static plane of the pipe. The mass flow rate is then a function of pipe geometry constants and the time interval determined by the up-down counter.
The invention of the present apparatus includes sensing means connected to two vibrating U-shaped tubes for sensing which side of the U-shaped tubes cross the static plane first, and timing means for timing the interval between the sides of the U-shaped tube passing through the static plane. The time intervals of successive half cycles of vibration are then combined based upon which side of the tube crossed the static plane first as determined by the mentioned sensing means.
The invention of the apparatus also includes peak vibration controlling means for controlling the peak amplitude of the vibration of the U-shaped tubes; proximity switching means within said sensing means for sensing when the sides of the tubes cross the static plane; and discriminator means for generating a pulse after the signal from the switching means reaches a predetermined level. This amplitude controlling means, switching means and discriminator means provide that the generated pulses from the discriminator means occurs after the output of the switching means is linear and holds the peak to peak amplitude of the tubes at a constant value during varying density of fluid for activating the switching at the same point of its operating characteristic curve.
Also disclosed is a means which compares with present time measurement with a set of a plurality of previous measurements for either rejecting or accepting the present time measurement depending upon whether the present time measurement falls within a given range of deviation from the mentioned previous plurality of measurements. Also included is a means for alternately selecting one value from a plurality of deviations for making the mentioned comparison.